For example, in the case of forming a resin molded article with a single wall structure, vacuum molding or pressure molding is performed such that after a thermoplastic resin original fabric sheet prepared in advance has been reheated to a molten state, the sheet closely contacts a die cavity by vacuum suction or air pressure. Vacuum molding or pressure molding has characteristics such as a characteristic suitable for high-mix low-volume production. Moreover, the applicant of the present application has developed a molding technique including bringing each of two extruded resin sheets into close contact with a corresponding one of dies in a pair by vacuum suction and subsequently clamping the dies to integrate these two resin sheets together.
In this type of vacuum molding or pressure molding, the heated molten resin sheet needs to be reliably in close contact with a cavity surface of the die. With poor close contact of the resin sheet with a die cavity, the surface shape of the die cannot be sufficiently transferred. For this reason, a resin molded article with predetermined quality cannot be obtained.
Meanwhile, the die shape has been diversified due to resin molded article diversification. For this reason, it is difficult to perform vacuum suction for the resin sheet in some cases. For bringing the resin sheet into close contact with the die cavity, vacuum suction is performed after a tip end of the die has contacted the resin sheet. However, in this state, the resin sheets contacting the dies need to form a closed space.
Among the above-described various dies, there is, however, a die having a parting line in a complicated (three-dimensionally curved) shape, for example. In this case, a clearance is also formed between the die and the resin sheet stacked in contact with the die. That is, there is a problem that it is difficult to form the closed space.
In view of such a situation, an attempt has been made to modify the die for forming the closed space. For example, JP-A-2012-192521 discloses a molding device configured so that thermoplastic resin extruded in a sheet shape from an extruding machine can closely contact a frame positioned at the periphery of a die. This molding device is configured such that a tip end surface of the frame is in a single plane. With this configuration, even when the shape of a parting line of the die is complicated, a resin sheet is arranged in contact with the frame, thereby forming a closed space. As a result, vacuum suction can be reliably performed.
Moreover, JP-A-5-16218 discloses a vacuum molding die used for bonding, at the same time as vacuum molding, a skin material in the form of a thin sheet to a surface of a base material set on the vacuum molding die, the base material being in a shape having a recessed surface portion at a substantially center portion. A frame protruding higher than an outer edge portion of the base material is provided at a portion of the vacuum molding die positioned at an outer peripheral portion of the set base material. It is described that upon vacuum molding of the skin material set on the frame, molding is performed such that the skin material comes into contact with the recessed surface portion in advance of the outer edge portion of the base material.